1. Field of the Invention
This invention relates to a method for fabricating a semiconducting nitride film, a susceptor and an apparatus for fabricating a semiconducting nitride film which are preferably usable for semiconductor films to construct semiconductor devices or optoelectronic devices such as light-emitting diodes and high velocity IC chips.
2. Related Art Statement
Group III nitride films including elemental Al are employed as semiconductor films constituting light-emitting diodes, and recently, win a lot of attention as semiconductor films constituting high velocity IC chips to be used in cellular phones.
Such Group III nitride films are usually fabricated by MOCVD methods using Al raw material including trimethylaluminum (TMA) or triethylaluminum (TEA) as gas and nitrogen raw material gas such as ammonia.
In this case, a substrate on which a Group III nitride film is formed is set on a susceptor tray installed in a given reactor and then heated to 1000xc2x0 C. or over by a heater built in the susceptor tray or provided outside the susceptor tray. Thereafter, Al raw material gas and nitrogen raw material gas are supplied with a carrier gas onto the substrate.
Through thermochemical reactions, the raw materials are resolved into their components, which are chemically reacted, to deposit and fabricate a desired Group III nitride film on the substrate.
FIGS. 1 and 2 are a perspective view and a cross sectional view showing the arrangement of a substrate on a susceptor tray, respectively, when a semiconducting nitride film is fabricated on the substrate by a MOCVD method.
As shown in FIGS. 1 and 2, a given recessed portion 15 is formed at the center of a susceptor tray 10, and a substrate 20 is set in the recessed portion 15. Since the size of the susceptor tray 10 is much larger than that of the substrate 20, the substrate 20 can be heated uniformly. After a given semiconducting nitride film is fabricated, the substrate 20 is released from the susceptor tray 10, and post-processed.
In the practical manufacturing process of semiconducting nitride films, the susceptor tray 10 is fixed in a reactor of a MOCVD apparatus, and a plurality of substrates 20 are set into the recessed portion 15 continuously in turn. Then, semiconducting nitride films are fabricated on the substrates 20, and the substrates 20 are released from the susceptor tray 10 in turn. Therefore, during a given operation period, debris of the semiconducting nitride films, which has a similar composition to the one of the film, may be deposited on the outer surface 10A of the susceptor tray 10.
If a large amount of debris is created, the step between the substrate 20 and the susceptor tray 10 is changed, so that the flow condition of the raw material gases is changed. As a result, the fabricating condition is affected slightly, the properties of the resulting semiconducting nitride films are deteriorated.
If the debris contains many Ga elements, it can be etched and removed when the susceptor tray 10 is disposed in a hydrogen flow. However, if a plurality of semiconducting nitride films including many Al elements are fabricated, and thus the debris contains many Al elements, the debris can not be etched and removed in such a hydrogen flow.
During a long operation time, the properties of the resulting semiconducting nitride films including many Al elements are slightly changed, and thus, cannot be made stable.
When the fabricating step of forming the semiconducting nitride film is performed under a depressurized atmosphere, heat can not be transmitted to the substrate 20 from the susceptor tray 10, and thus, the temperature of the outer surface 10A of the susceptor tray 10 is higher than the surface temperature of the substrate 20, so that the above-mentioned raw material gases are thermochemically reacted in a gas phase and deposited on the outer surface 10A. As a result, the fabricating efficiency and the property of the semiconducting nitride film is deteriorated due to the intense reaction of the raw material gases at the outer surface 10A.
It is an object of the present invention to repress deterioration of the properties of the semiconducting nitride film due to the debris created on a susceptor tray during fabrication of semiconducting nitride film.
In order to achieve the above object, this invention relates to a method for fabricating a semiconducting nitride film, comprising the steps of:
preparing a susceptor tray constructed of a base plate and an outer member,
setting a substrate in the recessed portion formed by disposing the outer member on the base plate, and
fabricating a semiconducting nitride film on the substrate.
In the fabricating method of the present invention, a substrate is set on the base plate of a susceptor tray so as to be surrounded by the outer member of the susceptor tray which is separately provided from the base plate. Therefore, the substrate can be heated uniformly by a heater built in or provided outside the susceptor tray, and a given semiconducting nitride film is fabricated on the substrate as usual.
In this case, the debris of the semiconducting nitride film is deposited on the outer member of the susceptor tray. However, since the outer member is detachable for the base plate of the susceptor tray, if the debris is deposited to some degree, only the outer member is taken out and washed, to remove the deposited debris easily.
If the outer member is made of a material of low optical absorption coefficient, that is, an optically transparent material of high transmissivity, the heating of the outer member due to radiation is inhibited, and thus, the reaction of raw material gases on the outer member, which results in the deterioration in the property of semiconducting nitride film, can be inhibited.
Also, since the outer member is exchangeable, a new outer member can be substituted for an old one, so that semiconducting nitride films can be made stable without washing.